AlanF said:
Much is being made about the weight reduction by Sony without the use of DO and that the centre of gravity of their lens is closer to the camera. But, look at the length of the 400/2.8 G Master, 359mm vs 233mm for the 400mm DO II. The Canon lens is 126mm, 5", shorter and so has the advantage of a c of g close to the camera. The DO technology will make other Canon supertelephotos shorter than the Sony counterparts.
But once again, you’re comparing an orange to a Granny Smith apple – Sony’s 400mm
f/2.8 G to Canon’s 400mm
f/4 DO. Would DO make Canon’s 400/2.8 shorter, sure...but until such a lens is actually produced and sold, discussing it in the context of a comparison is rather premature.
As I stated above, comparing lenses that differ by a stop of aperture isn’t very useful or reasonable, either. The Canon 400/4 DO also has a big advantage in size/weight/CofG compared to Canon’s 400mm f/2.8L IS II. But it’s a stop slower.
Meanwhile, for an apples to apples comparison...
Canon 400mm f/2.8L IS II: 343 mm and 3850 g
Sony 400mm f/2.8 GM OSS: 359 mm and 2895 g
The Sony is very slightly longer, but 25% lighter and better balanced. That’s a win for Sony. Can Canon beat it? To do so, they’ll have to repeat their improvement from the 400/2.8 IS MkI to MkII, which was a 28% drop in weight (similar to the improvement to the 600/4...whereas the 300/2.8 and 500/4 lenses saw much less of a drop in weight for their MkII iterations).